Electric double-layer capacitors have been used as electric energy storage devices which can be charged and discharged repetitively. Electric double-layer capacitors are advantageous over secondary batteries that use an electrochemical reaction, in that high-speed charge/discharge using a large amount of current is possible and that they have long service life.
Japanese Patent Laid-Open Publication No. Hei 4-154106 discloses technology related to electric double-layer capacitors. In this related art, an electric double-layer capacitor body formed by alternately layering positive and negative electrodes having a flat plate shape with a separator being disposed between these electrodes is put away in an enclosure in a state where the electric double-layer capacitor body is immersed in an electrolyte solution. A lead portion extending from a charge collector in the plurality of positive and negative electrodes is joined to an external terminal disposed on a cover of the enclosure.
At the time of charging/discharging of an electric double-layer capacitor, impurities or the like present in an electrolyte solution cause generation of gas, which then increases the pressure in the interior of the enclosure. In the related art described above, due to such an increased pressure or corrosion in the interior of the enclosure, the joint portion between the external terminals and the cover of the enclosure is damaged and deteriorated, which makes it impossible to maintain the sealing property in the interior of the enclosure. This leads to a problem that the electrolyte solution leaks, to thereby degrade the characteristics of the electric double-layer capacitor. The above related art also suffers from a problem that the increased pressure within the enclosure causes deformation of the enclosure.
The present invention advantageously provides an electric double-layer capacitor with an enhanced sealing property in the interior of an enclosure, an electric energy storage device including such an electric double-layer capacitor, and a manufacturing method of an electric double-layer capacitor. The present invention further advantageously provides an electric double-layer capacitor which can prevent leakage of an electrolyte solution even with an increase in the pressure in the interior of the enclosure, thereby preventing deformation of the enclosure.